My cousin got married a month ago and I made all her wedding invitations. I made 350 invitations, plus 3 insert cards for the invitations. I have a few tips.
1. Buy your cardstock from Anchor Paper. Especially if you are buying metallic paper, you will save a TON of money. Paper and More and Cut Cardstock both quoted me around $90 for enough paper to make the bases of the invitations. Anchor Paper quoted me $45.53 for all of the purple shimmer cardstock. Literally half the price, and that was WITH the cutting fee.
Shop at Anchor Paper
2. Have your cardstock cut to the size you need it. It will save you endless time over cutting it yourself.
3. Get helpers but choose ones who either follow directions well or know something about crafting. Don't recruit too much help, or it becomes stressful trying to make sure they all do the assembly correctly.
4. Give yourself plenty of time so you aren't rushed. Do the project in stages. Sort the paper one day. Score it one week. Emboss next, etc.
5. Invest in a scor-pal if you don't already have one. It will make scoring go much, much faster over other methods.
7. Buy a rubber stamp with your return address or print them on the computer. It saves lots of time.
8. Make a sample and weigh it, including envelope and insert cards. Reduce the weight if you can, to keep your postage costs low.
All told, it cost about $125 for all the materials, including adhesive and envelopes, to make 350 invitations, not including postage. We kept the weight down and paid only for one stamp on each envelope. We bought the envelopes from Anchor paper as well.
My cousins' wedding invitations are in my gallery - here is one of them:
Purple Wedding Invitation #3 by cardsbynikki - Cards and Paper Crafts at Splitcoaststampers